Hurricane Matthew killed 1,000 people in Haiti and at least 19 in the United States before downgrading to a post-tropical cyclone.

The storm moved out to sea Monday after hitting the coasts of North Carolina and Virginia, staying clear of the Northeast, the National Hurricane Center said.

Matthew, the most powerful Atlantic storm since 2007, made landfall near McClellanville, South Carolina, a village 30 miles north of Charleston, on Saturday, after slamming the coasts of Florida and Georgia with strong winds and rain.

Haiti started burying some of its dead in mass graves in the wake of Hurricane Matthew, a government official said on Sunday, as cholera spread in the devastated southwest and the death toll from the storm rose to 1,000 people.

The official death toll from the central civil protection agency is 336, a slower count because officials must visit each village to confirm the numbers.

Authorities had to start burying the dead in mass graves in Jeremie because the bodies were starting to decompose, said Kedner Frenel, the most senior central government official in the Grand'Anse region on Haiti's western peninsula.

Frenel said 522 people were killed in Grand'Anse alone. A tally of deaths reported by mayors from 15 of 18 municipalities in Sud Department on the south side of the peninsula showed 386 people there. In the rest of the country, 92 people were killed, the same tally showed.

Frenel said there was great concern about cholera spreading, and that authorities were focused on getting water, food and medication to the thousands of people living in shelters.

Cholera causes severe diarrhea and can kill within hours if untreated. It is spread through contaminated water and has a short incubation period, which leads to rapid outbreaks.

Government teams fanned out across the hard-hit southwestern tip of the country over the weekend to repair treatment centers and reach the epicenter of one outbreak.